Glossary

An objective measure of sharpness which takes into account the sensitivity of the human visual system to specific spatial frequencies and the viewing distance of an image. Edge acutance refers to the ability of a photographic system to show a sharp edge between contiguous areas of low and high illuminance. Texture acutance refers to the ability of a photographic system to show details without noticeable degradations.

Artifact created by the presence of frequencies in the image that are too high compared to the sampling frequency of the sensor. Staircasing-effects or Moiré patterns are two different forms of aliasing.

The most used pattern of photosites for color cameras, named after its creator, a researcher at Kodak in 1976. Photosites are grouped by four, with two sensitive to green wavelengths, one to blue wavelenghts, and one to red wavelengths.

Set of phenomena following which a point-wise light source is not imaged on the sensor on a single pixel. It is due primarily to optical causes and sensor integration. If the light source moves during the integration time, the phenomenon is known as motion blur.

Estimation of the specific parameters of a device; for example, the main calibration parameters of a sensor are sensitivity, spectral responsitivity, and noise; the main parameters of a lens are distortion, vignetting, chromatic aberration and MTF.

Light source or beam whose rays are parallel. A point-wise light source positioned at a lens focal distance provides a collimated beam. A very far point-wise light source, such as a star other than the sun, can also be considered as a collimated beam.

A two-dimensional array of colored filters placed on top of a sensor that allow the color of the input light to be recorded. Each photosite outputs a value that depicts the light in a subset of the visible spectrum. The most-used color filter array is the Bayer array.

Process that transforms the color values of the captured scene into digital RGB values displayed on an output device (screen, printer). By extension, also designates the process that transforms raw sensor values into displayed RGB values.

Coordinate system representing the visible colors, under a given illuminant. The L* coordinate represents the luminance, while a* and b* represent color (respectively the green-magenta axis and the blue-yellow axis). The Lab color space was designed to be perceptually uniform, meaning that a same distance between two colors should be perceived as the same difference whatever those colors are.

CSF is a functional description of the human visual system threshold sensitivity to the contrast (i.e. peak-to-peak luminance difference) of sine wave patterns of a range of spatial frequencies. The Contrast Sensitivity Function (CSF) is dependent on the viewing conditions, i.e. viewing distance, size of the displayed image and luminance viewing conditions.

Optical elements that absorb light used to simulate different levels of illumination. They are usually chosen to be as neutral as possible (i.e. their absorption is independent of wavelength) so that they do not change colors but only intensity.

Distortion is the variation of the magnification of the lens throughout the image field. In practical terms, photographic distortion describes the degree to which a lens cannot render straight lines in a scene as straight lines in the final image. Read more about how distortion is defined, measured and scored.

Algorithm used to reduce the dimension of an image. According to information theory, down-sampling needs to be performed so that it cancels frequencies too high (over Nyquist frequency) to avoid aliasing.

The DxOMark Score reports average lens-camera performances over the whole focal length and aperture ranges.

The DxOMark Score is reported using a gauge that shows the score itself as well as the range of scores over the focal range. WIth this gauge, photographers can view the homogeneity of the lenses image quality over their focal range.

The DxOMark Score is measured for defined exposure conditions corresponding to low-light scene with 150 lux illumination and an exposure time of 1/60s. These conditions were chosen as we believe low-light performances are very important for today’s photography and it is also important for photographers to know how well lenses perform at the widest aperture.